Experimental study on sound and damaged mortar: Variation of ultrasonic parameters with porosity

The relationship between porosity and ultrasonic parameters of mortar was studied. In order to enhance the sensitivity of the ultrasonic wave to microstructural changes, a high frequency range, 0.6–1.2 MHz, was chosen. The material investigated consists of four mortar mixtures with water/cement ratio varying from 0.3 to 0.6. Samples were chemically damaged for 4 periods of time (4, 9, 16 and 25 days). All the samples were degraded using a chemically accelerated process with an ammonium nitrate solution. This procedure yields a wide range of porosity values, from 10% to 35%. This growth of porosity was mainly attributed to the portlandite dissolution followed by C–S–H decalcification. The experimental results obtained showed that for sound samples, the correlation between physical and acoustic parameters yields the expected trend: velocity decreases with porosity. Secondly, the increase of porosity with the duration of degradation did not affect this relation between acoustic parameters and porosity where the latter remains linear.